A ball grid array (BGA) is a known example of a semiconductor package bonded to a printed circuit board. The BGA is bonded to a printed circuit board by means of the solder bumps.
As electric power is supplied into the semiconductor package and to the printed circuit board as a result of power-on operation and the electric power is interrupted as a result of subsequent power-off operation, the semiconductor package and the printed circuit board are subjected to cyclical temperature changes. Such temperature changes result in development of stress within the solder bumps owing to plastic strain therein. The degree of plastic strain increases with the number of power-on/off operations of an electronic circuit which includes the semiconductor package and the printed circuit board. The plastic strain occurs each time the electronic circuit is powered on or off. When the plastic strain reaches a limit value, the solder bumps break, making it impossible for the electronic circuit to operate normally.
Also, as the number of input/output terminals of semiconductor packages has increased owing to improved performance of electronic equipment in recent years, there is a tendency today for semiconductor packages to be of increased size. The larger the size of the semiconductor package, the more considerable the difference between the thermal expansion coefficients of the semiconductor package and the printed circuit board constructed of different kinds of materials, and the larger the plastic strain in the solder bumps. Accordingly, an increase in the size of the semiconductor package results in a reduction in the number of power-on/off operations at which breakage of the solder bumps occurs, and in a reduction in the number of years of service life of the electronic equipment employing the aforementioned type of electronic circuit. While such a problem is particularly noticeable in BGA-type semiconductor packages, the problem can occur in all electronic circuits including a semiconductor package and a printed circuit board bonded by solder bumps.
A method of preventing the aforementioned plastic strain problem is to keep electronic equipment operating at all times without powering off (and on) the equipment. Another technique for preventing a rapid change in the temperature of an electronic circuit is to preheat the electronic circuit before power-on.
However, operating the electronic equipment ceaselessly to prevent the plastic strain as in the aforementioned method continuously supplies electric power to the equipment. Furthermore, if the electronic equipment is a server apparatus used as an information processing apparatus in which plastic strain is to be avoided, for example, there arises a problem that running a fan for dissipating heat produced by the operating apparatus and an air conditioner for keeping a room where the server apparatus is located at a desired room temperature, thereby consuming additional electric power. Also, although it is possible to prevent rapid changes in the temperature of the electronic circuit by the aforementioned preheating approach, plastic strain in the solder bumps may occur because this approach is not intended to decrease a temperature difference caused by power-on/off operations.
Patent Document 1Japanese Laid-open Utility Model Application Publication No. 1985-042795